1. Field of the Invention
The present invention relates to a method and apparatus for synchronous operation of a plurality of injection molding devices which associate in producing a composite molding product, wherein the plurality of injection molding devices are synchronously operated by exchanging signals therebetween.
2. Description of the Related Art
There is known a composite molding product which is formed by assembling a plurality of components molded by using a plurality of injection molding devices, respectively. In a formation of such a composite molding product, it is significantly difficult to operate the plurality of injection molding devices at the same cycle time, for the following reasons: Namely, even where the plurality of injection molding devices are arranged for molding the components whose configurations are substantially similar to each other, masses of molten resin stored in injection devices of the injection molding devices have respective temperatures which are slightly different from each other, leading to difficulty in informing molding conditions such as an injection time and a cooling time of the injection molding devices. Moreover, the plurality of injection molding devices require respective period of times for executing a mold opening and closing actions, which period of times vary depending on structures and characteristics of the injection molding devices. Therefore, the cycle times of the plurality of injection molding devices inevitably deviate from the nominal value by a several percent.
In the presence of the deviation of the cycle times, one injection molding device whose cycle time is relatively shorter than that of the other injection molding device(s) is likely to produce more components than the other injection molding device(s) do. Since the components molded by the respective injection molding devices are assembled together to provide the composite molding product, it becomes a problem how to deal with surplus components molded by the injection molding device of shorter cycle time. In particular, for producing a digital video disk (DVD), for example, two injection molding devices produce respective component disks, and these two component disks are integrally bonded to each other at respective bonding surfaces to provide a bonded composite disk used as the DVD. In this case, the two injection molding devices are required to substantially simultaneously produce the component disks to be integrally bonded together to form the DVD. If this requirement is not satisfied, the resultant DVD may suffer from defects such as bending or buckling thereon. Therefore, the surplus components have to be disposed, undesirably. To solve this drawback, it can be envisioned to compensate a molding condition of the injection molding device of shorter cycle time so as to fit to that of the injection molding devices of longer cycle time, at appropriate opportunities during injection molding operations. However, such a compensation of the molding condition is not practical in view of significant difficulty in keeping a desired molding condition for a long period of time as described above. Besides, it can also be envisioned to once suspend operation of the injection molding machine, if an integrated value of deviation of the cycle times of the injection molding devices exceeds a value of one cycle time of the injection molding device of shorter cycle time. However, long-term suspension of the operation of the injection molding device causes undesirable change of temperature of a mass of molten or plasticized resin material stored in the injection apparatus of the injection molding device. Thus, the injection molding device is incapable of forming desired components for a while, after the operation of the injection molding device is resumed. This drawback may similarly occur, when any of the injection molding device comes to a standstill for some reasons.
The present invention has been developed in view of the circumstances described above. It is therefore a first object of the present invention to provide a method of synchronously operating a plurality of injection molding devices which associate in producing a composite molding product, by exchanging signals therebetween.
It is a second object of the invention to provide an injection molding system suitable for practicing the method indicated above.
The first object may be achieved according to one aspect of this invention, which provides a method of synchronously operating a plurality of injection molding devices which associate in producing a composite molding product, comprising the step of: simultaneously initiating a predetermined action in the plurality of injection molding devices, on the basis of an initiation timing of the predetermined action in one of the plurality of injection molding devices whose initiation timing of the predetermined action is latest in the plurality of injection molding devices.
The first object may also be achieved according to another aspect of this invention, which provides a method of synchronously operating a plurality of injection molding devices which associate in producing a composite molding product, wherein each of the plurality of injection molding devices includes: a control device having a signal output port for transmitting an initiation standby signal of a predetermined action thereof and an signal input port for receiving the initiation standby signal of the predetermined action of the other injection molding devices, and actuators for driving an injection device and/or a mold clamping device thereof so as to execute the predetermined action of the corresponding injection molding device, the method comprising the steps of: operating the control device to transmit the initiation standby signal of the corresponding injection molding device through the signal output port; operating the control device to generate an initiation signal of the corresponding injection molding device, when the control device receives the initiation standby signals of the all other injection molding devices and generates the initiation standby signal of the corresponding injection molding device, so as to actuate the actuator, whereby the corresponding injection molding device execute the predetermined action.
The second object indicated above may be achieved according to a yet another aspect of the present invention, which provides an apparatus for synchronous operation of a plurality of injection molding devices, comprising: a plurality of injection molding devices each including a control device having a signal output port for transmitting an initiation standby signal of a predetermined action thereof and an signal input port for receiving the initiation standby signal of the predetermined action of the other injection molding devices, and actuators for driving an injection device and/or a mold clamping device thereof so as to execute the predetermined action of the corresponding injection molding device, the control device being operable for transmitting the initiation standby signal of the corresponding injection molding device to the other injection molding devices through the signal output port, and being operable for receiving the initiation standby signals of the all other injection molding devices, while being operable for ANDing all of the initiation standby signals received by and generated in the control device, so as to transmit an initiation signal to the actuator, thereby actuating the actuator to execute the predetermined action of the corresponding injection molding device.